This report represents my first set of observations with the SSP-4 (1mm detector). What I have tried to accomplish with this set of observations is to refine my observation technique so that I can make accurate and repeatable measurements. I feel this goal has been accomplished, that is, the SSP-4 photometer is capable of repeatable measurements with a predictable accuracy. I plan to add to this report as I gather more observations. In my next phase of observations I will concentrate on determination of the color transformation coefficients, airmass extinction terms, and the signal-to-noise (SNR) dependence with magnitude.

Table 1 presents the results of differential photometry measurements taken with the Optec SSP-4 (1mm detector). The telescope used was a Meade 0.25m SCT in alt-az configuration. The column labeled "Comp SNR" and "Target SNR" represents the SNR of the comparison and target stars, respectively. The SNR is calculated from the ratio (average counts for n measurements)/(standard deviation for n measurements). The measurements in table 1 have not been corrected for color and airmass differences between the target and comparison stars. The SSP-4 detector temperature is assumed to be -40C unless noted. For some measurements I added a flip mirror mounted to the telescope. The flip mirror functioned as a right angle prism. Adding the flip mirror caused a decrease in the flux by approximately 0.5 magnitude. I used the flip mirror to increase the altitude of stars that I could observe. In the "straight through" configuration, that is, without the flip mirror, the SSP-4 will strike the telescope for stars with altitudes approximately 50 degrees or higher.

Table 1 - SSP-4 Differential Photometry

UT

UT

Comp Star

Intg

Comp

Target

Target

Target

Date

Time

Name

Filter

Gain

Time

SNR

SNR

Mag

Notes

5/6/03

2:15

Spica

J

10

5

42

Del Vir

47

-0.31

1

5/6/03

2:15

Spica

H

10

5

49

Del Vir

104

-1.10

1

5/6/03

2:10

Spica

J

10

5

42

Arcturus

147

-2.30

1

5/6/03

2:10

Spica

H

10

5

49

Arcturus

133

-2.98

1

5/6/03

2:35

Spica

J

10

5

79

Del Vir

91

-0.32

1

5/6/03

2:35

Spica

H

10

5

35

Del Vir

92

-1.16

1

5/6/03

2:45

Spica

J

10

5

25

Del Vir

221

-0.36

1

5/6/03

2:45

Spica

H

10

5

43

Del Vir

103

-1.07

1

5/9/03

2:15

SAO 119035

J

10

5

22

SAO 156605

20

1.71

2

5/9/03

2:15

SAO 119035

H

10

5

71

SAO 156605

40

1.02

2

5/9/03

2:15

SAO 119035

J

10

5

22

SAO 138238

17

2.04

2

5/9/03

2:15

SAO 119035

H

10

5

71

SAO 138238

43

1.28

2

5/9/03

2:15

SAO 119035

J

10

5

22

Spica

10

1.61

2

5/9/03

2:15

SAO 119035

H

10

5

71

Spica

12

1.84

2

5/9/03

2:15

SAO 119035

J

10

5

22

SAO 156605

14

1.74

2

5/9/03

2:15

SAO 119035

H

10

5

71

SAO 156605

42

1.25

2

5/9/03

2:45

SAO 119035

J

10

5

25

SAO 156605

14

1.58

2

5/9/03

2:45

SAO 119035

H

10

5

51

SAO 156605

42

0.84

2

5/9/03

2:45

SAO 119035

J

10

5

25

SAO 138238

15

1.88

2

5/9/03

2:45

SAO 119035

H

10

5

51

SAO 138238

53

1.21

2

5/12/03

1:55

Spica

J

10

5

42

SAO 139033

53

1.36

3

5/12/03

1:55

Spica

H

10

5

56

SAO 139033

118

0.29

3

5/12/03

2:05

Spica

J

10

5

15

SAO 139033

51

0.90

3

5/12/03

2:05

Spica

H

10

5

32

SAO 139033

122

0.16

3

5/12/03

2:20

Spica

J

10

5

157

SAO 139033

128

1.16

4

5/12/03

2:20

Spica

H

10

5

104

SAO 139033

241

0.32

4

5/12/03

2:30

Spica

J

10

5

45

SAO 139033

31

1.23

4

5/12/03

2:30

Spica

H

10

5

193

SAO 139033

152

0.33

4

5/15/03

2:00

Spica

J

10

5

36

SAO 139033

64

1.16

5

5/15/03

2:00

Spica

H

10

5

62

SAO 139033

183

0.30

5

5/15/03

2:10

Spica

J

10

5

44

SAO 139033

59

1.09

5

5/15/03

2:10

Spica

H

10

5

60

SAO 139033

118

0.31

5

5/15/03

2:35

Spica

J

10

5

41

SAO 139033

71

1.10

5

5/15/03

2:35

Spica

H

10

5

66

SAO 139033

101

0.08

5

Table 1 Notes

Clear, T(amb) = 70F, no flip mirror, averaged over six integrations

Clear, humid, T(amb)=80F, with flip mirror, average over seven integrations

Clear, full moon, T(amb)=70F, without flip mirror, average over seven integrations

Table 2 - Catalog Magnitude for Stars in Table 1

Star

Spectral Type

J

H

Source/Note

SAO 105223

K3II

0.32

-0.38

Standard - UKIRT/Henden

Spica

B1III

1.51

1.58

UKIRT

Del Vir

M3III

-0.13 to -0.31

-.09 to -1.13

Gezari+ 1999

Antares

M1.5Ib

-2.40 to -3.13

-3.47 to -.377

Gezari+ 1999

Arcturus

K1.5III

-2.18 to -2.52

-2.81 to -3.05

Gezari+ 1999

Altair

A7V

0.39

0.25

UKIRT

SAO 139033

M3III

1.19

0.32

UKIRT

SAO 119035

M1III

1.05

0.25

UKIRT

SAO 156605

G8III

1.68

1.07

UKIRT

SAO 138238

K3III

1.33

1.16

UKIRT

Conclusions:

Repeatable observations can be taken with the SSP-4.

Using the 05/12 and 05/15 observations with Spica as the comparison star and SAO 139033 as a target star you obtain for SAO 139033: J = 1.14 +/- 0.05 and H = 0.26 +/- 0.04. The error term is the standard deviation of the mean for seven measurements. These J and H values are within 1.5*error of the published values for SAO 139033. This is reasonable when you consider both catalog J and H magnitudes for Spica and SAO 139033 have an error of 0.05 mag and are both small amplitude variable stars. This also indicates that the color correction terms will be small since these two stars are of very different color.

In this report I develop the relationship between the signal-to-noise (SNR) and the error in magnitude for a single five second integration with the SSP-4. The SNR is calculated from the ratio (average counts for n measurements)/(standard deviation for n measurements). Note that the standard deviation is for a single measurement not for the mean. For the observations shown in figures 1 and 2, n was seven or eight, in other words, I took seven or eight five second integrations per band. The sky background count was an average of three five second integrations. The telescope used was a Meade LX200 0.2m SCT and the observing setting is suburban. I can typically see 4+ magnitude stars naked eye near zenith. Figures 1 and 2 show the dependence of the SNR upon the magnitude of the star.

In table 1, the columns labeled “J Band SNR” and “H Band SNR” represents the average SNR that would be expected for stars with magnitudes between -2 and 4. These numbers are derived from the exponential formulas contained in figures 1 and 2. The columns with labels “J Band Error” and “H Band Error” represent the expected error (one sigma) associated with each value of SNR. The formula for calculation of the estimated error is 1.0857/SNR.

Table 1 - Estimated SNR and Error as a Function of Magnitude

J Band

J Band

H Band

H Band

Mag

SNR

Error

SNR

Error

-2

456

0.00

196

0.01

-1

255

0.00

148

0.01

0

143

0.01

111

0.01

0.5

107

0.01

96

0.01

1

80

0.01

84

0.01

1.5

60

0.02

72

0.01

2

45

0.02

63

0.02

2.5

33

0.03

55

0.02

3

25

0.04

47

0.02

3.5

19

0.06

41

0.03

4

14

0.08

36

0.03

A couple of general comments. I need to complete figures 1 and 2 with observations for stars fainter that 2.5 magnitude. In figure 2, the SNR drops lower than would be expected for stars brighter that 0th magnitude. I am not sure if this an observational problem or an instrumentation problem or just an odd coincidence. More observations are needed to clarify these points. In my next report I will cover color the transformation coefficients and the airmass extinction parameters.

In this report I present my initial observations with the SSP-4 and a 0.25 SCT through 17 June 2003. My observation technique is as follows:

Set gain =10, Detector temperature = -40 C, and integration time = 5 seconds. Set dark current greater than 100.

Eight observations with J filter of star

Three observations of sky with J filter

Eight observations with H filter of star

Three observations of the sky with H filter.

Next star and repeat steps 2-5.

In a typical observation session, each star is measured at least twice in each filter band. Each observation has been reduced with the Henden and Kaitchuck Astronomical Photometry Software For IBM-PC. This software takes into account color differences between the comparison stars and airmass differences.

Table 1 contains my first set of observations with the photometer. Each of the column headings is self explanatory except for the “Est Error” column. The error estimated by taking the standard deviation of the mean. Taking at least two observations per target and using two comparison stars results in at least four estimates of the target magnitude. The standard deviation of the mean of these multiple observations becomes the estimated error. All of the observations in table 1 have been submitted to the AAVSO or ALPO.